The present invention relates to a control system for an inter-axle differential, and more particularly, to a method of calibrating such a control system.
In order to improve turning radius and traction during turning, front wheel drive tractors have been provided with actively controlled slip interaxle differentials. U.S. Pat. No. 5,301,769, issued to Weiss on 12 Sep. 1994, describes a vehicle power distribution and control system wherein the slip of an inter-axle differential is controlled as a function of steering angle of the steerable front wheels and wheel rotation speed.
U.S. patent application Ser. No. 09/151,348 filed 20 May 2002 (docket no. 15630-US), now abandoned, describes a control system for controlling the modulating clutch of an interaxle differential which transmits torque from an engine driven transmission to a front axle and to a rear axle. The differential includes a planetary gear set coupled to the modulating clutch. The modulating clutch is coupled between a pair of the planetary gear elements, and is used to bring the front to rear speed differential within desired limits. The control system operates in response to sensed steering angle, sensed front wheel speed, sensed rear wheel speed and calibration values stored in a look-up table. From these factors the control system determines a desired maximum speed difference between the front and rear wheels, and controls the differential to keep the front to rear speed ratio within the desired limit. The clutch is modulated to “feather” the differential action to deviate from “normal” differential action when the front (or rear) wheels are on slick ground and the rear wheels have good traction. The primary reason for this condition is when the load is such that the tractor weight is shifted to the rear wheels and the front end is coming off the ground.
However, different tractors may have different tires, and a control relationship which works well for one tractor may not function optimally for a tractor with different tires. As a result, the above-described differential control system had to be manually calibrated and the look-up table values determined for optimum operation for each individual tractor. But, conditions and sensor responses also change over time. It is desired to have a differential clutch control system which automatically adapts to different unique vehicles and which adapts to changes in vehicles and sensors.